This study is designed to examine the effects of center and family day care of varying quality on the psychological development of one- and two-year-old children. The major questions of the study are: 1. Does day care have an effect on any of the following aspects of early psychological development: attachment to the mother, response to unfamiliar adults, compliance to the mother, cooperation with and compliance to unfamiliar adults, exploration in a novel setting, reaction to frustration, problem solving behavior, maternal perception of the child, or maternal maturity expectations? 2. Does family day care differ from center day care in its effects? Are the effect of day care mediated by the quality of the care or the number of hours in care? Does unstable care differ from stable care in its effects? 5. Are the effects of day care mediated by any of these child characteristics: sex, age at day care entry, SES, or prior separation experience? The sample consists of 222 children between 12 and 24 months old at the time they enter the study. The sample is divided into five groups matched on a number of demographic variables: Center Day Care (N equals 50), Family Day Care (N equals 42), Unstable Day Care (N equals 30) and two Home-reared Comparison groups, one whose mothers are positively disposed toward day care (N equals 60) and one whose mothers are negatively disposed toward day care (N equals 40). The day care children were pretested before their first day in day care and posttested five months and nine months later.